1. Field of Use
This invention relates generally to apparatus and methods for removing and disposing of fluid material accumulated on a surface located below a body of liquid, such as sludge accumulated on the floor of a large liquid storage tank used to store liquid petroleum or chemical products or such as sand or silt accumulated on a surface underlying a body of water.
In particular, the apparatus includes a self-propelled, computer-controlled cleaning machine which is disposed on the floor of the storage tank or on the surface beneath a body of water and to control means for operating the cleaning machine.
The method pertains to procedures for operating the cleaning machine to carry out a cleaning routine, to store retrievable data pertaining to the cleaning routine and to prevent unauthorized use of the cleaning routine.
The invention is particularly well-suited for use in cleaning sludge from large liquid storage tanks and is described herein in that context, except as hereinafter noted.
2. Description of the Prior Art
Storage tanks are use for storing liquid petroleum products, such as crude oil received directly from an oil well or refined petroleum products such as fuel oil, gasoline or the like, prior to transport or distribution. Such tanks are typically fabricated of steel plate about one-half inch thick and are mounted on a concrete base or platform and take the form of a cylinder on the order of 100 or more feet in diameter and 50 or more feet in height. Such a tank comprises a circular floor, a cylindrical side wall and a hemispherically-shaped top wall or cover, which may or may not be vertically movable relative to the side wall to take into account the amount of product in the tank. The cover is provided with a manhole or access opening, typically about three or more feet in diameter, which has a removable manhole cover to enable access to the interior of the tank for purposes of inspection, service and cleaning.
Over time, foreign substances suspended in the liquid product in the tank settle out by gravity to form a layer of fluid material, such as a viscous sludge, on the floor of the tank ranging in size from several inches to a foot or more in depth. Periodically, this sludge must be removed from the tank so as to prevent it from contaminating liquid products subsequently added to the tank and, depending on the composition of the sludge, to prevent it from corroding and damaging the steel floor and wall of the tank. For example, sludge from crude oil typically contains sand, stone chips from drilling, bits of metal worn off of the well drill bit, viscous lumps of parafin, sulfur, and water which condenses in the tank. Sludge from refined petroleum products may contain some of the above-described debris, as well as dirt and rust from other tanks and pipe-lines through which the refined product has passed, and condensed water.
Heretofore, tank cleaning was accomplished by draining the liquid product from the tank and having personnel enter the tank through the manhole with those tools necessary to scrape up and pump out the sludge to a collection tank located exteriorly of the storage tank. Needless to say, the atmosphere in an empty petroleum storage tank is highly explosive and highly toxic. Therefore, stringent government and industry regulations govern the type of cleaning equipment (explosion-proof) and protective equipment (protective garments, breathing gear) which must be employed. Prior art manual cleaning procedures require a large work-force and several weeks to carry out and, of course, the tank is empty and out of service during this period. It is apparent, therefore, that prior art storage tank cleaning procedures are extremely hazardous to personnel, make-shift as regards equipment, labor-intensive, unduly time-consuming and exceedingly costly.
Similarly, certain types of dredging operations carried out beneath a body of water to remove sand or silt heretofore required a diver who manipulates a dredging pump on the floor or bed beneath the body of water to remove unwanted accumulations of sand, silt or sludge-like materials. Again, a skilled professional, diver is required and needs to be provided with elaborate life-support equipment. Furthermore, the diver may be exposed to a hazardous and/or toxic environment, and is employed in a time-consuming, labor-intensive and costly pursuit.